Theory of Operations
AIRMAR
TECHNOLOGY CORPORATION
35 Meadowbrook Drive, Milford, New Hampshire 03055
Tel 603 -673-9570 • Fax 603-673-4624• www.airmar.com
17-256-01 Rev. 01
AIRMAR
TECHNOLOGY CORPORATION
Theory of Operations
Contents
I. Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
A. Airmar Technology Corporation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
B. Echosounder Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
C. Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
D. Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
E. Piezoceramic Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
F. Sound Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
G. The Structure of Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
H. Performance Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
I. Airmar Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
J. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Theory of Operations
The purpose of this booklet is to inform you about the products that are designed
and manufactured by Airmar and give you a basic understanding of how they work
and how they are used. Our customers depend upon us for products that meet their
requirements. As a member of the Airmar Team, your quality work is a vital part of
meeting those requirements and contributes to maintaining Airmar’s leadership
position in the transducer industry.
The information in this booklet will help you to better understand how significant what
you do is, and how it fits into the overall picture. Included is a glossary of frequently
used scientific terminology. If you have any questions not answered by this booklet,
please submit them to your manager.
1
Theory of Operations
Airmar Technology Corporation
What is Airmar?
Designers, engineers, and scientists develop the products.
Assemblers on the manufacturing floor produce the sensors and a full line of parts and accessories. All this activity
is supported by shippers, receivers, maintenance people,
and business personnel.
Airmar Technology Corporation was founded in Amherst,
New Hampshire in 1982 by two engineers, Stephen G.
Boucher and Robert K. Jeffers. Airmar moved to Milford in
1987 where it continues to grow as a leader in the transducer industry.
Who are Airmar’s customers?
At Airmar, we pride ourself on our ability to work hand-inhand with our customers to fulfill their specific requirements with the highest quality products. This may be
done with one of our existing products, a slight modification to a standard product, or an entirely new design.
Airmar has a world-wide customer base of Original
Equipment Manufacturers (OEMs). Our sensors are
bought to be coupled with the OEM’s electronics. Usually,
the OEM sells the system to the public with its name on
the label.
Airmar’s first product in 1982 was a simple, marine, ultrasonic transducer. Today, marine transducers remain the
core of our product line with over 1,000 transducer part
numbers available. We now offer:
While many of our customers are echosounder producers,
we have customers in other industries as mentioned earlier. Some of our customers include:
• Recreational sensors for echosounders, fishfinders, and
personal watercraft
• Raytheon
• Commercial fishing transducers for vessels of all sizes
• Yamaha
• Large navigation and survey transducers for use on ships
and research vessels
• Odom
• Aquaculture systems
• Lowrance
• Air transducers for industrial uses
• Standard Communications
• Furuno
• Hycontrol
• Interphase
Airmar holds over twenty-five United States and foreign
patents. We have won the important Innovation Award
presented by the International Marine Trade Exhibition
Conference for the first truly low-cost phased array transducer developed for use in marine environments. This
transducer allows electronic steering of the ultrasonic
beam giving the user the ability to gather more
information.
• Kawasaki
• Bombardier
We also sell to one after-market distributor, Gemeco. This
company sells replacement transducers as well as marine
accessories to the public.
2
Theory of Operations
Echosounder Systems
What is an
echosounder system?
transceiver generates high voltage electrical pulses and
sends them to the transducer. The transducer converts
these pulses into sound waves that bounce off objects
underneath the boat, then echo back to the transducer.
The transducer converts the sound energy of the echo to
an electrical pulse which is returned to the echosounder.
The echosounder measures the time between the beginning of a pulse of sound and the return of the echo. The
microprocessor then “reads” this information, translates it,
and presents it on a display screen in a way that depicts
the bottom, any objects, and the location of
any fish.
An echosounder system is specialized equipment which
gives a boater or fisher the ability to see below the surface of the water. It gives information about the depth
and shape of the bottom and of any fish present.
An echosounder system is made up of two major parts.
The first is the echosounder. This includes a display screen
to present the information, the transceiver to drive the
transducer and receive echo information, and a microcomputer to process
the information.
Different echosounders display information in
different ways. A flasher type echosounder
displays illuminated bars of varying intensity
to depict the depth of the water and any
objects in the water. A digital echosounder
displays the bottom depth in numbers or letters. Echosounders with LCD and CRT screens
display the information in a “picture” form.
The second key part is the transducer. It
generates sound waves and receives the
echoes of those sound waves. The information is fed from the transducer
through cables to the echosounder
which interprets and presents the information in an understandable form on
the display screen.
What part of the echosounder
system does Airmar produce?
How does an echosounder
system work?
Airmar produces the transducer—the underwater sensor for the echosounder system.
All echosounder systems work in essentially the same way. The echosounder
Transducers
What is a transducer?
ducer then converts the transmit pulses into sound. The
sound travels through the water as pressure waves. When
a wave strikes an object like a weed, a rock, a fish, or the
bottom, the wave bounces back. The wave is said to
echo—just as your voice will echo off a canyon wall.
The transducer is the heart of an echosounder system. It is
the device that changes electrical pulses into sound waves
or acoustic energy and back again. In other words, it is the
device that sends out the sound waves and then receives
the echoes, so the echosounder can interpret or “read”
what is below the surface of the water.
When the wave of sound bounces back, the transducer
acts as a microphone. It receives the sound wave during
the time between each transmit pulse and converts it back
into electrical energy. A transducer will spend about 1% of
its time transmitting and 99% of its time quietly listening
for echoes. Remember, however, that these periods of time
are measured in microseconds, so the time between pulses
is very short.
How does a transducer work?
The easiest way to understand how a transducer functions
is to think of it as a speaker and a microphone built into
one unit. A transducer receives sequences of high voltage
electrical pulses called transmit pulses from the echosounder. Just like the stereo speakers at home, the trans-
3
Theory of Operations
How does a transducer
know what the bottom
looks like?
As the boat moves through the water, the
echoes of some sound waves return more
quickly than others. We know that all
sound waves travel at the same speed.
When a sound wave in one section of
the sound field returns more quickly than
another, it is because the wave has
bounced off something closer to the
transducer. These early returning sound
waves reveal all the humps and bumps in
the underwater surface. Transducers are
Transducer transmitting pulses
Transducer receiving echoes
able to detect whether a bottom is soft or
hard and even distinguish between a
The echosounder can calculate the time difference
clump of weeds and a rock, because the sound waves will
between a transmit pulse and the return echo and then
echo off of these surfaces in a slightly different manner.
display this information on the screen in a way that can
be easily understood by the user.
How does a transducer see a fish?
The transducer can see a fish, because it senses the air
bladder. Almost every fish has an organ called an air bladder filled with gas that allows the fish to easily adjust to
the water pressure at different depths. The amount of gas
in the air bladder can be increased or decreased to regulate the buoyancy of the fish.
How does a transducer
know how deep the water is?
The echosounder measures the time between transmitting
the sound and receiving its echo. Sound travels through
the water at about 4,800 feet per second, just less than a
mile per second. To calculate the distance to the object,
the echosounder multiplies the time elapsed between the
sound transmission and the received echo by the speed of
sound through water. The echosounder system interprets
the result and displays the depth of the water in feet for
the user.
Because the air bladder contains gas, it is a drastically different density than the flesh and bone of the fish as well
as the water that surrounds it. This difference in density
causes the sound waves from the echosounder to bounce
off the fish distinctively. The transducer receives the
echoes and the echosounder is able to recognize these
differences. The echosounder, then, displays it as a fish.
4
Theory of Operations
Frequencies
What is frequency?
hear. Humans can hear sound waves from 10 Hz to 20
kHz. Most fish are unable to hear frequencies higher than
about 500 Hz to 1 kHz. The ultrasonic sound waves sent
out by Airmar transducers have frequencies ranging from
10,000 kHz to 2 Megahertz (200,000,000 Hz), clearly
beyond the hearing of fish. However, most people can
hear the transmit pulses of our 10 kHz transducers; they
sound like a series of clicks.
Frequency is the number of complete cycles or vibrations
that occur within a certain period of time, typically one
second. Sound waves can vibrate at any one of a wide
number of frequencies. The easiest way to understand frequency is to think of it in terms of sounds that are familiar.
For example, a kettle drum produces a low-pitched sound
(low frequency). That is, it vibrates relatively few times per
second. Whereas, a flute produces a high-pitched sound
(high frequency). It vibrates many more times per second
than a kettle drum.
How does the frequency of a transducer
determine what we see?
The frequency of sound waves is measured in a unit
called a Hertz. A Hertz is one cycle per second. For example: a 150 kHz transducer operates at
150,000 cycles per second.
A higher frequency transducer will put out quicker, shorter, and more frequent sound waves. Like the ripples made
when a small pebble is thrown into
still water, small waves of sound
move evenly out and away from the
source. Because they are just small
waves, they will not travel far and
small obstacles will cause them to
bounce back. Higher frequencies
are more sensitive to small objects
and will send back detailed information which will show as crisp, highresolution pictures on the
echosounder screen. The range of
high frequency sound waves, however, is short. In fact, sound waves
emitted by a 200 kHz transducer
have a limited range of about 600
feet.
Is the frequency of all
transducers the same?
No, transducers can be designed to
operate efficiently at any number of
specific frequencies depending upon
the application and performance
requirements of the customer. Airmar
transducers are often designed for 50
kHz (50,000 cycles per second) or
200 kHz (200,000 cycles per second).
Can fish hear the sound
waves produced by a
transducer?
Now, think of the large waves created by a large boulder thrown into
still water. Low frequency sound
waves are like these large waves;
they travel much farther than high
No, the sound waves are ultrasonic.
They are above (ultra) the sound
(sonic) that human ears are able to
Higher Frequency
Lower Frequency
Number of waves or cycles per second
more
fewer
Wave length
shorter
longer
Detail
more detail, small objects
less detail, large objects
Depth Capacity
shallow to moderate
deeper
5
Theory of Operations
The speed of sound in water is
4,800 feet per second. If we
have a 200 kHz transducer then
our equation would look like
this:
4800 ft/sec ÷ 200,000 cyc/sec =
0.024 ft/cyc = 0.29 inches/cyc
One sound wave at 200 kHz is
slightly longer than 1/4 of an
inch, so a 200 kHz sound wave
will be able to detect fish as
short as a quarter of an inch.
Let us compare the 200 kHz
transducer to the size of a wave
length of a 50 kHz transducer:
Higher frequency waves
4800 ft/sec ÷ 50,000 cyc/sec =
0.096 ft/cyc = 1.15 inches/cyc
Lower frequency waves
One sound wave at 50 kHz is
slightly over one inch, so a 50
kHz sound wave will only detect fish if their air bladders
are large, slightly longer than an inch.
frequency waves. But because low frequency waves are
so large, they wash right over small obstacles. Low frequency sound waves are not as sensitive in detecting
small fish or other small obstacles as are high frequency
waves, and although they can see to greater depths,
they will not send back detailed information or clear
crisp pictures.
How does a customer decide what
frequency is needed?
Why is it important to know the length
of a sound wave?
A higher frequency sound wave will give the user a higher resolution picture of what is present under the water,
but the range will be short. Fishers in more shallow lakes
who want a crisp clear picture of the bottom need a higher frequency transducer.
Knowing the length of sound waves is particularly important, because it determines where the sound waves will
bounce. A sound wave will bounce strongly off something that is larger than itself. If the object is smaller, then
the sound wave will almost wash over the object, and the
echo will be very weak.
Low frequency sound waves will not give the user as clear
a picture of the bottom, but they have greater range for
very deep areas where high frequency sound waves cannot reach. A low frequency unit will work well in the
depths of Lake Michigan or the ocean. You may find the
chart on page 5 helpful.
The length of a sound wave is determined by the frequency of the sound vibrations and the density of the medium
that the sound is traveling through. At Airmar, wave
length is calculated by dividing the speed of sound in
water by the frequency.
6
Theory of Operations
Piezoceramic Elements
What are piezoceramic elements?
Like a piece of china that has been fired in a kiln, the
piezoceramic element is very strong, yet brittle and easily
cracked or broken. Any piezoceramic element that has
been cracked or chipped, even slightly, will not function
properly in a transducer.
The main component of a depth transducer is the piezoceramic element. It is the part that converts electrical pulses into sound waves, and when the echoes return, the
piezoceramic element converts the sound waves back into
electrical energy.
Coating—After pressing, the piezoceramic element is coated on two opposite sides
with a layer of silver and
baked a second time, so
the silver actually bakes
onto the element. This silver functions as the electrode, the material that
will conduct electric current through the element.
Airmar does not manufacture its own piezoceramic elements, because their manufacture is a very specialized
process. Instead, we buy piezoceramics from companies that make
them to our specifications.
What does a
piezoceramic element
look like?
Polarizing—Next the
piezoceramic element is
polarized. Piezoceramic
elements are made up of
individual crystals that have a positive (+) and negative (–)
electric charge on respective ends. These crystals are normally resting in a haphazard way in the piezoceramic element. But if a high voltage electric current is applied to
the element, the crystals will adjust their alignment until
nearly all are positioned in straight columns with their
positive (+) and negative (–) poles lying in the same
direction.
Piezoceramic elements are most
often in a disk form, but they may
also be in the shape of a bar or a
ring. A transducer may contain
one element or a series of elements linked together called
an array.
What are piezoceramic
elements made of?
Most of the piezoceramic elements
that we use in our transducers are
made of Barium Titanate (BT) or
Lead Zirconate Titanate (PZT).
Note: Since this process is done in an oil bath, it is very
important that the piezoceramic element has all of the oil
carefully removed or the potting material will not bond
to it. A weak bond will result in poor transducer performance and poor reliability.
How are piezoceramic elements made?
The BT and PZT elements go through several processes
before Airmar receives them.
How do piezoceramic elements work?
Remember, transducers work by taking electrical pulses
from the echosounder and changing them into sound
waves. This process is reversed when the transducer is
acted upon by the pressure of the returning echoes which
is called transduction.
Pressing—Both BT and PZT begin in powdered form. The
powder is pressed into the desired shape.
Firing—The pressed shapes are baked in a kiln just like we
might fire a clay pot made in an art class. The temperature of the kiln depends upon the element’s maximum
heat tolerance. It is important to fire the piezoceramic at
precisely the right temperature.
The internal arrangement of the piezoceramic element’s
crystals with their positive (+) and negative (–) poles lying
7
Theory of Operations
in the same direction is the key
factor. Pulses of alternating current (AC) from the echosounder
activate the piezoceramic element. The AC changes its direction of flow back and forth.
[Which is why it is said to alternate, and this change in the
direction of the flow is noted as
(+) and (–).] Because the piezoceramic elements are polarized, they
will expand when a positive voltage is applied and contract when
a negative voltage is applied.
The piezoceramic’s expansion and
contraction changes the electrical
pulse into sound waves that will travel through the water
until they bounce off an object or weaken and finally
dissipate.
Piezoceramic expands
when + voltage applied
Piezoceramic contracts
when - voltage applied
resonant frequencies. The size,
shape, and thickness of the
piezoceramic element determine
the frequency at which it will
vibrate best. Engineers very carefully control these factors to produce transducers that resonate at
the correct frequency to meet the
customers’ needs.
Most of the piezoceramic elements that Airmar uses are thickness resonant. The thickness
dimension of the piezoceramic
element, rather than its diameter
or shape, determines the
resonant frequency.
A transducer can be designed with one piezoceramic that
operates at two frequencies. Our popular 50/200 kHz
transducer houses a piezoceramic element that can
vibrate efficiently at two separate frequencies. It resonates
at 200 kHz in the thickness mode and at 50 kHz across its
When an echo returns to the transducer, the pressure of
the sound waves act on the piezoceramic element causing it first to contract and then to
expand as each cycle in the echo hits it.
This alternating pressure on the element
creates a small voltage which is then
sent back to the transceiver and microprocessor.
The element expands and contracts at
Vibrates
Vibrates
Vibrates
the frequency of the electrical pulse. This
across the diameter
across the thickness
across the thickness
and the diameter
occurs very rapidly, faster than can be
seen by the eye. The frequency of the
diameter which is called the radial mode. A transducer
expansion and contraction is controlled by the frequency
that can operate at two frequencies will have the characof the pulse generator in the echosounder.
teristics of both frequencies—the ability to “see” well in
both shallow and deep water with good bottom
How do the engineers know which
definition.
piezoceramic element to use?
When an electrical voltage is applied to a piezoceramic
element, it will vibrate best at a certain frequency.
Piezoceramic materials can be thought of as bells. When a
bell rings, it produces a tone. Each bell has its own natural resonant frequency. Those who cast bells know the size
and shape necessary to create a bell that produces a certain tone.
What is capacitance?
Capacitance comes from the word capacity. It is the ability
of a material to store an electrical charge. Piezoceramic
elements are first class capacitors, able to hold a large
electrical charge. In fact, the larger the piezoceramic the
larger the charge that can be stored.
Knowing that piezoceramic elements store a charge and
Like bells, every piezoceramic material has its own natural
8
Theory of Operations
piezoceramics, their ability to store an electrical charge
can be used to our advantage. With a simple capacitance
meter, we can test the piezoceramic after wires have been
soldered in place and the cable has been attached. If a
wire connection is faulty, only a small capacitance will
show on the capacitance meter. A much larger capacitance will show if the piezoceramic is wired properly. This
is an easy check of the manufacturing process.
that even slight cooling and heating will build-up an electrical charge, means that all piezoceramics must be handled with great care. Production workers must always
short a piezoceramic before handling it. If this is not done,
the piezoceramic may discharge, damaging other components in a multi-sensor transducer or even giving the handler a very nasty, albeit harmless, shock.
In spite of the precautions that need to be taken with
Sound Waves
How do the sound waves
travel in the water?
ic, the wider and
less concentrated
is the sound
beam. For example, the beamwidth produced
by the smaller,
one inch, piezoceramic will “see”
fish over a large
area, whereas a
larger, two inch,
piezoceramic will
provide a narrower beamwidth
giving better bottom definition and detection of small fish
in shallow water.
Understanding wave motion can help you understand
the way in which transducers work. When you throw a
pebble into still water, you can see small ripples or waves
form around the spot where the pebble entered the
water. If you watch closely, you will see these circular
ripples or waves move evenly away from the center. When
waves move in this manner, they are said to move in
concentric circles.
When sound waves are transmitted, they too begin to
spread out as they make their way deeper into the water.
Because the sound waves have been transmitted under
the boat, they are moving downward and outward in concentric circles. Since the downward and outward movement is happening at the same time, the waves are actually making a cone shape. This is referred to as the radiation
pattern. Thinking of the sound waves transmitted from a
transducer as an ice cream cone turned up side down will
help visualize the sound field for a typical singleceramic transducer.
How much underwater area can be seen
by an echosounder?
Engineers determine how wide an
area will be seen on the water’s
bottom by knowing the depth of
the water and the transducer’s
cone angle. If you have a mathematical calculator or trigonometry
tables, you can calculate
beamwidth using the following
formula:
How wide is the radiation pattern
made by a transducer?
We refer to the widest part of the cone-shaped radiation pattern as the beamwidth. It is the diameter
of the outer most circle of sound waves. Engineers
are able to increase or decrease the beamwidth and
therefore the area that the transducer can “see”.
(2 x depth) x (tangent of 1/2 cone
angle) = diameter of the beam
(beamwidth)
One way to change the beamwidth is to use piezoceramic elements of different diameters. The larger
the piezoceramic, the smaller and more concentrated is the sound beam; the smaller the piezoceram-
9
Theory of Operations
the rings of light will
be dimmer. These rings
are the sidelobes of the
flashlight beam.
The chart on the bottom of this page shows this concept.
There are several ways to specify beamwidth. The commercial fishing and naval industry frequently provide
beamwidth information by measuring the sound beam at
–3 dB. The marine recreation industry, however, provides
beamwidth information measured at
–6 dB, giving the impression that their
transducers have a wider beam field.
When engineers design
transducers,
they calculate
what sidelobes
are present. In
fact, 60% to
70% of the
sound waves
will be concentrated in the
cone area and
the remaining waves will escape in all directions.
What is target masking?
There are areas within the transducer’s
range which seem to be invisible to
the echosounder. This is known as target masking. It can happen if the lake
or sea bottom drops off suddenly or
contains a large rock. The sound
waves will bounce off all of the sea
bottom within the sound beam and
return as strong echoes. The echoes
from the highest point, the rock or
drop-off, return to the transducer first, falsely indicating
the apparent depth of the bottom. Small fish below the
highest point will produce relatively small echoes which
will return after the larger ones. Therefore, fish can be
swimming around the sides of a large rock or a drop-off,
be in the sound field, and yet remain invisible to the
echosounder.
Engineers generally like to minimize sidelobes,
although they may actually be desirable in some
situations. As with a flashlight, a transducer does
not “see” as well in the sidelobes, because fewer
of the sound wave echoes return to the transducer. Fish might be present in this area, but a fisher would
be unaware of them. However, in the case of a narrow
beam transducer, sidelobes can be useful, since they effectively widen the coverage.
What are sidelobes?
Sidelobes are typically presented as part of the transducer’s radiation pattern. The lower, smaller, and narrower the
sidelobes, the better the transducer performs, because
more of the sound waves are focused in the main beam.
Our engineers are concerned about a phenomenon called
sidelobes. You can see sidelobes for yourself by using a
flashlight. If you shine a flashlight against a wall, you will
see an area at the center where most of light is
concentrated. Around the edge of the flashlight beam,
Sidelobes are watched carefully during product development. Each transducer model creates its own particular
sidelobe pattern as the sound waves travel through the
water. This information is very important to those who
design the echosounders to be used with our transducers.
Diameter of Viewable Area or Beamwidth
Cone Angle
Depth in Feet
5
10
25
35
50
9°
16°
18°
20°
32°
45°
53°
0.8
1.4
1.6
1.7
2.8
3.9
4.6
1.6
2.8
3.1
3.5
5.6
7.9
9.2
3.9
7.0
7.9
8.7
14.0
19.6
23.1
5.5
9.8
11.0
121.2
19.5
27.5
32.4
7.9
14.0
15.7
17.4
27.9
39.3
46.2
10
Theory of Operations
The Structure Of Transducers
What goes into the making
of a transducer?
and provides a water-tight seal to minimize any possibility
of water entering the unit.
It is clear that the transducer would not work without the
piezoceramic element, however, other parts are also needed. A transducer is made up of six separate components:
What is an acoustic window?
The acoustic window is the surface through which the
sound waves travel. It occupies the space between the
piezoceramic assembly and the water. Any material used
to create the acoustic window will absorb some of the
sound waves that pass through it. Therefore, engineers
carefully choose the least absorbent materials. The
acoustic window is sometimes referred to as the
acoustic face.
• Piezoceramic element or an array of elements
• Housing
• Acoustic window
• Encapsulating material
• Sound absorbing material
• Cable
Epoxy, plastic, and urethane are the three materials Airmar
uses most often for our acoustic windows. These materials
have sound wave carrying capabilities or acoustic
properties between those of the piezoceramic element
and water.
What is the housing
of a transducer?
The housing is the container that covers, protects, and
supports the component parts of the transducer. The
piezoceramic element is very brittle, and the wire connections to the piezoceramic are fragile. Because of this, the
housing needs to be sturdy as well as resistant to the
chemical, mechanical, and electrical forces in the environment where it will be used.
Acoustic window materials fall
into two categories.
Soft, rubbery, elastic materials like urethane carry sound
waves in almost the same manner as water. So, water and
urethane are said to have similar acoustic properties.
Because of this close match, the thickness of acoustic windows made from urethane does not need to be tightly
controlled in our product designs.
Our housings are made of a variety of materials and take
on different shapes depending upon the customer’s need
and intended type of installation. Some of the housing
materials are:
• Molded plastic
• Stainless steel
• Bronze
Hard materials like plastic and epoxy have acoustic properties somewhere between those of piezoceramic elements
and water. In other words,
the plastic or epoxy acts
like an intermediate
acoustic step between the
fluid water and the rigid
piezoceramic element.
• Urethane (SEALCAST™)
The plastic and urethane housings are
produced in our own
molding department.
Airmar’s custom SEALCAST ™ transducers
feature a seamless
housing and a compression fitting at the
cable exit. This compression fitting secures
the flexible cable at
the point of attachment to the housing
A plastic or epoxy acoustic
window is called a matching layer. Layer thicknesses
are carefully calculated
and produced to match
the sound wavelength at
the operating frequency.
11
Theory of Operations
How will air bubbles interfere
with transducer function?
In what other ways do acoustic
windows differ?
Because air is much less dense than water, air bubbles
scatter and reflect sound waves. Any air bubbles in the
acoustic window material or in the water will interfere
with the proper working of the transducer, greatly reducing its performance. To minimize the chance for tiny, flecklike, micro-bubbles in the acoustic window material, it is
placed under a vacuum for a specific amount of time.
Acoustic windows can be “hard” or “soft.” Soft acoustic
windows made of urethane provide excellent sensitivity to
echoing sound waves, therefore soft windows can “read”
through deeper water with better clarity of detail. This
material is extremely stable in water, therefore providing
excellent reliability for years. Because the acoustic properties of urethane are similar to water, the acoustic window
can be made in the shape of a dome, wedge, or an arc.
Air bubbles must, also, be carefully guarded against by
the installer and user. If the transducer is glued to the
inside of the hull of a boat, even the glue cannot have air
bubbles in it. Indeed, a transducer needs to be placed
away from anything, including the propeller, that will
cause air bubbles to form while the boat is underway.
Hard plastic and epoxy acoustic windows are especially
good for boats that are trailered or often in and out of the
water, because these windows become wet quickly. They
also have characteristics which are good in shallow water
and in fishfinding.
What will interfere with an acoustic
window’s ability to become wet?
What is the encapsulant?
The encapsulant is the material that encases the parts of
the transducer within the housing. It can act as an
acoustic window material, filler, or sealant. At Airmar the
encapsulant is often called potting material and includes
epoxies and urethanes. The choice is based upon its ability to meet the performance and application requirements
of the particular transducer design.
In order for a transducer to work correctly, the surface of
the acoustic window must be thoroughly wet. How quickly the acoustic window becomes wet depends, in part,
upon the type of material used to make it.
Glossy surfaces, such as our plastic and SEALCAST™ urethane acoustic windows, wet almost instantly, because
they are smooth.
Our sanded urethane acoustic
windows take
much longer to
Sanded, urethane, acoustic window (magnified)
become thoroughly wet. Although the sanded
urethane does not seem rough to the touch, the sanding
process leaves microscopic peaks and valleys which
trap air bubbles keeping the water from touching the
urethane.
Because of this, transducers with sanded urethane
acoustic windows would have to soak in water for a minimum of one hour before testing their ability to transmit
and receive. In order to shorten this process, our testers
lightly scrub the urethane window with alcohol in order
to hasten the wetting process. Both the scrubbing and
the alcohol help to quickly displace the microscopic air
bubbles.
What is sound absorbing material?
Sound absorbing material is any material that interrupts or stops the flow of sound waves. In our
case, it is the material used to dampen any
unwanted vibrations of the piezoceramic element
in a transducer.
When AC voltage is applied to a piezoceramic element,
all surfaces of the element vibrate. This means it sends
off or radiates sound waves in all directions. Therefore,
the piezoceramic element could pick-up echoes returning
from all directions giving false information to the echosounder. This effect is called spurious radiation and must
be avoided.
To reduce spurious radiation as much as possible, the
piezoceramic element is surrounded with sound absorbing material, usually a layer of cork or foam. In this way
vibrations of the piezoceramic element are dampened on
all the surfaces except the surface facing the acoustic win-
12
Theory of Operations
dow. As a result, the sound waves are given directionality.
They are concentrated in one direction only. Directionality
is also effected by the piezoceramic’s shape and frequency.
snowy—the clarity and sharpness of the image is lost.
How do Airmar cables function?
Aluminum foil on Mylar
A transducer cable is the vehicle which carries the electrical current between the echosounder and the transducer.
It is usually made of several conductors or wires. Cables
are carefully engineered to carry a specified voltage and
current from the echosounder to the sensor(s) in the
transducer.
Tinned braided shield
Depending upon the application and performance
requirements for the transducer, several types of shielding
are used such as:
Spiral shield
The cables outer jacket protects the inner conductors and
provides strength and flexibility.
Jackets materials include:
PVC—polyvinyl chloride
Inside the jacket of each cable is shielding to protect
against electrical pulses from other electrical equipment
that could interfere in the workings of the transducer. This
interference is called electrical noise. Commonly heard as
static, electrical noise could come from
a ship-to-shore radio, navigation equipment, ignition impulses, or even
another transducer. Interference has
the same effect on the echosounder
display screen as it does on a television screen; the picture becomes
TPR—thermoplastic rubber
Neoprene
Polyurethane
Performance Testing
What is performance testing?
This information is known as performance data which is made
available to customers and used
as the standard for final testing
of the product. The figures are
extremely important to our OEMs
as this data is used to determine
the frequency at which the
echosounder must
be set.
Airmar products are designed to a customer’s specifications or to fill a market
need. Engineers most often begin with a
required frequency and cone angle. After
the transducer is designed, a sample is
built in the lab where it is extensively tested. Data is collected on:
• Frequency
• Beamwidth
Airmar products are tested many
times during their manufacture
and are subjected to a careful
final inspection. A wide variety of
test equipment, including our
test tanks, is used.
• Transmitting Voltage Response (TVR)
• Receiving Voltage Response (RVR)
• Figure-of-Merit
• “Q” (Bandwidth)
• Ringing
• Impedance
13
Theory of Operations
What are the Transmitting
Voltage Response
and the Receiving Voltage
Response?
As we know from the Receiving
Voltage Response, the returning
sound wave will be far weaker than
the original sound wave that was
sent out. This is because the transmitted sound wave looses energy by the
time it travels through the water,
bounces, and returns.
Each Airmar transducer model is tested to measure the strength of the
transmitted sound wave and the
received sound wave (what we have
been calling the echo).
Engineers test each transducer
model and graph the results of the
Transmitting Voltage Response, the
Receiving Voltage Response, and the
Figure-of-Merit. The graphed curve of
the Figure-of-Merit will usually peak
somewhere between the peak of the
Transmitting Voltage Response and
the peak of the
Receiving Voltage
Response.
The Transmitting Voltage Response
(TVR) is a measure of the acoustic
pressure of the sound wave at a distance of one meter when one volt of
electricity is applied to the transducer.
If we could hear the sound waves,
we might say the TVR is an indication
of how loud a sound the transducer
produces when one volt is applied to it.
The Receiving Voltage Response (RVR) is a measure of
the voltage produced within the transducer when a 1
mPa (micropascal) of acoustic pressure is received. An
mPa is a unit for measuring sound pressure. The pressure of the echoing sound waves causes the piezoceramic to produce voltage, the RVR. Think of a lamp that
can be turned on by the clap of hands. It is the loudness
of the clap, the pressure of the sound wave, that turns
on the lamp. If we could see the transducer’s response
to the echoing sound waves, we might say the RVR is
an indicator of how brightly the lamp shines.
What is “Q”?
“Q” stands for quality and is a measure
of the sharpness of
the response of the
piezoceramic element to the frequency that is supplied to it. In other
words, “Q”
describes how precisely the frequency
must be output to
achieve the best
performance from
the transducer. It answers the questions: “What is the
piezoceramic element’s best or resonant frequency?”,
“How well does the piezoceramic element work on either
side of its resonant frequency?”, and “How long will the
transducer continue to ring after a transmit pulse?”
Comparing the TVR and RVR shows that the difference
between the actual voltage used for transmitting and
the actual voltage generated by the returning echo is
tremendous. Sound waves are emitted by voltage measuring in the hundreds (100s) of volts, yet the returning
echoes are measured in hundredths (1/100s) of a volt.
What is the Figure-of-Merit?
The Figure-of-Merit is a measure of how well a transducer
works when used for both transmitting and, then, receiving its own echoes. It is the algebraic sum of the
Transmitting Voltage Response and the Receiving Voltage
Response. The Figure-of-Merit is sometimes referred to as
the Insertion Loss.
Engineers have a standard method for determining “Q”. It
is the operating frequency divided by the bandwidth. For
non-engineers, it is helpful to think of frequency and
bandwidth in terms of volume and tuning-in your favorite
14
Theory of Operations
What is Ringing?
Ringing is the continued vibration of the piezoceramic element after each transmit pulse. Imagine the ringing of a
large church bell. After the church bell is struck by the
clapper, it continues to ring for a time if the vibrations are
not dampened.
This phenomenon also occurs in piezoceramic elements.
The vibrations of the element continue after the transmit
pulse. These vibrations decrease in amplitude (or “loudness” if we could hear them) just as the ring of the church
bell gets softer over time. The tapering off of the vibrations is called the ring down.
radio station. The operating frequency is that spot on the
radio dial where your favorite station comes in the loudest
and clearest.
The bandwidth includes the frequencies slightly above
and below the best spot, but where the station can still
be heard. Engineers use the standard of three decibels
below the peak Transmitting Voltage Response, shown as
–3 dB. If we could hear the transducer sound waves, the
–3 dB point is where the sound would be half as loud. As
we turn the dial above and below our station, the signal
begins to fade, so we can’t hear it as well. The points
above and below the radio station on the dial at which
our radio is half the
volume of the correct
radio station frequency
determines our bandwidth.
In effect, ringing causes a “stretching” of the transmit
pulse, because it generates unnecessary sound waves.
These additional sound waves add additional microseconds to the dead band, interfering with the reception of
echoes.
If a desired echo arrives during the ring down it will
appear on the echosounder screen as a
smear or it may even be hidden by the ring
down and not appear on the echosounder
screen at all. Ringing, therefore, reduces the
clarity of the display on the echosounder
screen.
The “Q” of a transducer
model can be determined by analyzing its
Transmitting Voltage
Response graph. The
resonant frequency
and peak TVR is at 50
kHz. At 3 dB below
TVR, the frequencies
are 47.6 kHz and 52.8
kHz, giving us a bandwidth of 5.2 kHz (52.8
kHz – 47.6 kHz = 5.2
kHz). To determine “Q”,
the resonant frequency is divided by the bandwidth giving us a “Q” factor of 9.6. (50 kHz ÷ 5.2 kHz = 9.6).
Ringdown also keeps the transducer from
“seeing” in very shallow water.
Ringing can never be totally eliminated. With
the proper engineering, however, it can be
greatly reduced. A transducer with a high “Q”
factor is one which will ring for a long time
after being struck with a transmit pulse.
Conversely, a low “Q” transducer exhibits less
ringing.
How are the deadband and
blanking zone related?
As you have learned, during the transmit pulse the piezoceramic is vibrating, so no echoes can be received—in the
same way that you cannot listen when you are talking.
The microseconds when the transducer is transmitting is
the deadband for the reception of echoes.
“Q” factors range between 1 and 40. At 9.6 this model’s
“Q” factor is relatively low. The OEM need not be as precise in setting the echosounder’s drive frequency when a
transducer has a lower “Q”.
When something very close to the transducer (usually
between one and three feet), the bouncing echoes will
15
Theory of Operations
return before the piezoceramic has stopped ringing. Since
the echo is in the deadband, these echoes cannot be
received—the object will be invisible. The minimum distance between the transducer housing and an object that
can be “seen” is called the blanking zone. OEMs typically
want a small blanking zone, so their echosounders can
“see” objects close to the transducer.
quotient is the impedance.
The echosounder must be designed to match the impedance of the transducer to deliver the correct power to it. If
they do not match, the output from the transducer will be
reduced lessening the performance of the entire system.
Airmar chooses materials that are natural conductors of
electricity. Silver is used on our piezoceramic elements,
because it is an excellent conductor and is easy to apply
and bake onto our piezoceramic elements. Copper is used
in all electric wiring, because it is an excellent conductor
and less expensive than silver.
What is Impedance?
Impedance stems from the word impede and means
something that hinders progress. In the field of electricity,
it refers to the limitation of the amount of current that can
flow through a material. Impedance is technically the ratio
of voltage to current. Airmar measures the amount of
electrical force applied to the transducer and the amount
of current that actually runs through the transducer. The
Some materials will not allow electrons to flow through
them at all. These materials are called insulators. They are
used around all electrical wires to keep electricity flowing
through the conductor(s) and prevent electricity from
flowing elsewhere.
Airmar Products
How are Airmar products unique?
• Depth with Speed and Temperature (TRIDUCER ®
multisensor)
Airmar’s products incorporate the most advanced technology; often pioneered by Airmar. Our attention to detail
makes our sensors more accurate and reliable than the
competition. Careful design, manufacture, and testing
insures that our transducers perform to specifications. We
use waterproof connectors, multiple O-rings, seamless
construction, and strong materials to produce sensors that
can withstand harsh environments.
• Speed only
• Speed with Temperature
Recreational transducer housings come in several shapes
depending upon their intended method of installation.
In-hull—This transducer is installed against the inside of a
boat hull bottom and sends its signal through the hull.
Some people prefer this method, because the unit cannot
be damaged when the boat is trailered. Also, drilling
through the hull is not necessary. In-hull transducers can
work better than other models at high boat speeds.
What products does Airmar manufacture
in each product line?
Recreational Sensors—Our recreational transducers can
be manufactured to perform several different functions
when used with the appropriate information display unit.
Because in-hull units “shoot” through the layers of the
hull, there is a loss in performance. In addition, this installation will not work on a boat made of any
material containing air bubbles, because the air
bubbles reflect and scatter the sound before it
reaches the water. Wooden hulls and fiberglass
hulls with foam, balsa wood, or plywood layers
sandwiched between the inner and outer skins
are not recommended for in-hull installation.
Airmar sensors can measure:
• Temperature only
• Depth only
• Depth with Speed
Transom Mount—This transducer style is mounted to the back (transom) of a boat hull. Some
people prefer this style, because it affords easy
• Depth with Temperature
16
Theory of Operations
installation and removal of the unit—especially if a kick-up
bracket is used. A kick-up bracket allows the transducer
to be moved out of the way to prevent damage from a
boat trailer. A transom mount installation gives better performance than the in-hull installation at boat speeds up
to 30 MPH.
In our bronze transducer the temperature sensor is placed
inside the housing cavity because the metal housing itself
is a good thermal conductor. The bronze quickly takes on
the temperature of the water and, as a result, the temperature sensor doesn’t require direct water contact.
Thru-hull—This transducer is installed through a hole in
the boat and protrudes into the water. It is most often
used on boats 25 feet or longer and usually provides the
best performance. The transducer is low enough in the
water to avoid most of the air bubbles caused by the
motion of waves.
In a few other types of transducers a semiconductor temperature sensor is also used. Because the electrical voltage
put out by the semiconductor changes slightly with each
degree of temperature, the temperature of the water can
be determined by measuring the electrical voltage put out
by the semiconductor.
Thru-hull units are not recommended in two situations:
Speed Sensors
• Plastic thru-hull housings should not be used on a
wooden boat. Wood swells as it absorbs water, so it
may crack the housing.
Boat speed is measured in nautical miles per hour called
knots. A nautical mile is 6,076 feet, approximately 1.15
land miles.
• Bronze thru-hull housings should not be used in aluminum boats. The interaction between the aluminum
and the bronze especially in the presence of salt water,
will eat away the aluminum hull and/or bronze housing.
The component used to determine boat speed is called a
Hall Cell and works like an on/off switch. Within the sensor are magnetic parts that can be turned on and off by a
passing magnet. The Airmar paddlewheel blades are magnetized. As the boat moves through the water, the paddlewheel turns. Each time a magnetized blade of the paddlewheel passes by the Hall Cell, it is turned on or off, creating a pulse of electricity. Electronics in the echosounder
system count the frequency of these pulses, then convert
them into knots. A paddlewheel may create as many as
22,000 electrical pulses per nautical mile.
Temperature Sensors
Temperature sensors are desirable for several reasons.
Anglers know that fish prefer certain water temperatures,
so a temperature sensor can help the fisher determine
where the fish may be hovering. Boaters may wish to
know the water temperature before jumping in for a
swim, but more importantly, it can be a navigational aid.
For example, the water in the Gulf Stream is much warmer
than the surrounding Atlantic Ocean. Boats traveling north
are wise to locate and ride the current while those traveling south need to avoid the Gulf Stream entirely.
TRIDUCER® Multisensor
The Airmar TRIDUCER® multisensor is a combination of
three sensing devices built into one housing to measure
depth, speed, and temperature.
Temperature is most commonly read by a temperature sensor called a thermistor. The Airmar thermistor is a 10,000
ohm resistor which varies in value according to its temperature. This means that the amount of electricity flowing
through the resistor is directly related to the temperature
of the resistor. The warmer the resistor the more electricity
is able to flow through it. Conversely, less current is able to
flow through the resistor when it is cold. The amount of
electrical current flowing through the resistor, therefore,
tells us the temperature of the water.
Phased Array Transducer
A phased array transducer can function as both a downward looking and a forward looking transducer. It does
not point straight down only. Rather, the echosounder can
steer the beam about 45 degrees to either side. These
transducers are able to “see” both the immediate underwater depths and what is ahead of the boat. It can see both
a large schools of fish toward which a boater would like to
steer and large objects or a shallowing bottom to be
avoided.
Most of Airmar’s temperature sensing devices are built right
into the transducer housing.
17
Theory of Operations
Commercial Fishing Transducers
easy meal. The sound has been likened to the scratching
of fingernails on a blackboard.
The dB PLUS II™ Acoustic Deterrent System has a
unique “soft-start” feature. The system takes 25 seconds to
reach full power. This gradual sound increase provides a
warning to divers and allows seals and sea lions the
option of leaving the area before the sound reaches its
highest volume.
These transducers are available in frequencies from 24 kHz
to 200 kHz. Units feature high-efficiency designs producing superior fish finding and clear and distinct images of
both the bottom and closely spaced fish.
Navigation
and Ocean Survey Transducers
This product has been successfully used in waters off of
the U.S., Canada, Chile, New Zealand, and Europe. The
seals are keeping their distance, so the customers are
very happy.
This broad product group features transducers ranging
from 10 kHz to 2 MHz. Airmar offers transducers sized
from small portable units for harbor survey to multi-frequency arrays for deep sea sounding. Arrays of more than
100 piezoceramic elements have been designed and manufactured by Airmar. We can produce dual beam and split
beam transducers and linear phased, and multi-beam
transducer arrays.
Air Transducers
Air transducers work in a way that is very similar to
marine transducers. Air, however, is not as good a conductor of sound waves as water. In fact, sound travels
only 25% as fast in air as in water. Think of the time delay
between seeing lightning and hearing the thunder or
between your shout and its echo. Speed is not the determining factor in the loss of efficiency. Temperature,
humidity, and wind are the determining factors.
One hydrographic product specifically designed for a customer is the Swath bathymetry transducer. It’s transmitting
transducer uses a fan beam which is very narrow in one
directions and very broad in the other direction. Echoes
are received by 30 separate transducer elements which
form 30 separate beams. This provides 30 sets of data
yielding a great amount of detail about the bottom. One
Swath is used to monitor the ever shifting channels in the
Mississippi River.
Air transducers can be used in a variety of ways in both
commercial and industrial applications:
• Silo or tank level detection of liquids such as oil; or
of solids such as grain, coal, flour, or anything stored
in bulk
dB PLUS II™
Acoustic Deterrent System
• Proximity measurement
• Process control
The dB PLUS II™ Acoustic Deterrent System uses Airmar’s
skill at producing sound waves, to scare away marine life
rather than to find it. Our popular acoustic deterrent system is designed to protect fish farms from seals and other
marine predators who find the fish an inviting target.
• Object detection
• Volume of liquid flow through weirs
• Sensing through foams
• Level detection in waters with sediment such as septic
plants or in environments that are dusty
The acoustic deterrent system has a series of four transducers positioned around the fish pens which are made
of net. The transducers work as projectors only, giving out
sound waves for 2.5 seconds in turn. It takes 18 seconds
to complete one full four-transducer transmission cycle.
The amplifier for creating the electrical power supplied to
the transducers is centrally located among the net pens.
• Liquid column measurement
What are the characteristics
of air transducers?
Frequencies from 25 kHz to 225 kHz are available in our
air transducers.
Research tells us a sound wave frequency of 10 kHz is not
harmful to seals, but it is definitely irritating. Their desire
to get away from the sound overcomes their desire for an
Airmar’s models are designed to meet criteria set by hazardous environmental certification agencies. Because air
18
Theory of Operations
water around the transducer, so that drag on the boat is
minimized. All Airmar fairings are made from a polymer
resin which will not swell or rot.
has relatively low density, air transducers are susceptible
to ringing. The dead band specification is very important
to the OEMs and our engineers strive to design air transducers with low “Q” and, therefore, low ringing.
Our parts and accessory line includes:
• Housings, hull nuts, and cap nuts
Parts and Accessories
What is a Fairing?
• Switch boxes
A fairing is a structure which is added to the transducer at
the mounting location to improve its performance. If the
hull slopes, a fairing orients the transducer so the sound
beam will aim straight down. The chance of water with
air bubbles flowing across the acoustic window is reduced
by mounting the transducer deeper in the water. Also,
Airmar carefully designs the shape its fairings to direct
• Cables and connectors
AC the abbreviation for Alternating
Current. Electrical current that reverses
direction at regular intervals.
AC voltage used to cause the piezoceramic element to vibrate.
Acoustic relating to sound and sound
waves.
Acoustic Energy when work can be
done because energy is provided by the
physical pressure of a sound wave.
Acoustic Face see Acoustic Window
Acoustic Property the ability of a material to carry sound waves through it.
Acoustic Window that part of the transducer through which the ultrasonic vibrations from the piezoceramic assembly
travel to the water or other transporting
medium. It occupies the space between
the piezoceramic assembly and the water.
Air Bladder an organ in a fish which
allows it to adjust easily to changes in
water pressure at different depths. It is
the organ that allows the echosounder to
detect the fish.
Amplitude the degree of intensity (pressure) of a sound wave. If we could hear
the sound wave, the amplitude would be
its “loudness.”
• Mounting kits
• Speed sensor parts
• Fairings
• Diplexer
Glossary of Terms
Angler a person who fishes.
Application Requirement the use that
the sensor is designed for.
Array a series of piezoceramic elements
in a transducer.
Bandwidth the range of frequencies over
which the transmitting sensitivity (TVR) is
no less than one half of the peak sensitivity at –3dB.
Beamwidth the diameter of the circle
in which 50% to 70% of the sound
waves emitted by a transducer are concentrated.
Cable the wire that carries power
between the echosounder and the transducer. It is usually constructed of several
conductors.
Capacitance the ability to store an electrical charge.
Ceramic a commonly used name for the
piezoceramic element.
Concentric Circles a series of circles of
different sizes having a common center.
Conductor anything that carries electrical current. This may be a copper wire or
any other material that readily allows
electrons to pass through it.
19
Cone Angle the measurement of
beamwidth in degrees. It is an indication
of how large an area is covered by a
transducer’s sound beam. The larger the
cone angle the larger the area covered.
Current the measure of the number of
electrons that flow past a point in a specific unit of time.
dB an abbreviation for decibel. A unit for
measuring the power of a sound wave.
Deadband the time during and immediately after a transmit pulse when a transducer cannot receive echoing sound
waves and therefore cannot “see” the
area below the surface of the water.
Deadzone the minimum distance
between the transducer housing and an
object that can be “seen” by an
echosounder.
Directionality the controlled emission of
sound waves in the desired direction.
Display Screen the part of the
echosounder unit on which an image of
the underwater area is projected.
Drag the retarding force exerted on a
moving object.
Glossary of Terms
Echosounder an instrument comprised
of a display screen and electronic circuitry. It provides necessary power to the
transducer, interprets the information
received from the transducer, and
displays this information in a readable
format.
Echosounder System a system comprised of two major components—an
echosounder and a transducer. This system measures the depth of the water
and the distance to any objects in its
field of vision, and displays this information in a readable format.
Electrical Energy when work can be
done because energy is provided by an
electrical force.
Electrical Noise interference in an electronic signal, often called static.
Electrode a solid material which conducts electricity and is used at the point
where electrical current enters or leaves
an object.
Encapsulant the material that acts as a
filler in and around the transducer parts
within the housing. It may also function
as an acoustic window or a sealant.
Encapsulant is often called potting
material.
Energy a measure of a system’s ability
to do work.
Figure-of-Merit (FOM) the algebraic
sum of the Transmitting Voltage
Response and the Receiving Voltage
Response. The Figure-of-Merit usually
indicates a net loss of energy, and is
sometimes referred to as Insertion Loss.
Frequency the number of complete
cycles or vibrations that occur within a
specific time frame, typically one second.
It is usually measured in Hertz.
Hall Cell a wafer of silicon altered by
electrical current so that it responds
magnetically.
Hertz (Hz) a measure of one cycle or
complete vibration per second.
Housing something that covers, supports, or protects the mechanical parts.
Impedance the limitation of the
amount of flow of electrical current. It is
commonly used as a comparison
between the amount of voltage needed
to get a specific amount of current.
In-hull Installation the method of
installing a transducer by attaching it to
the inside of the hull.
Injection Molding the process of creating parts by forcing melted material
(usually plastic) into a mold in the
desired shape. The material is then
cooled and released from the mold.
Insertion Loss the algebraic sum of the
Transmitting Voltage Response and the
Receiving Voltage Response. This usually
indicates a net loss of energy. Often
referred to as the Figure-of-Merit.
Insulator any material that will not
allow electrons to pass through. These
materials are used to surround conductors to keep the current flowing in the
desired direction.
Jacket the covering that surrounds a
cable and provides strength.
Kilo-Hertz (kHz) one thousand cycles
or complete vibrations of sound per second.
Knots nautical miles per hour. A nautical
mile is 6,076 feet or roughly 1.15
statute miles.
Matching Layer an acoustic window
material like plastic or epoxy that has
acoustic properties somewhere between
those of the piezoceramic element and
the water. It acts as an intermediate
acoustic step and facilitates the travel of
sound waves from the piezoceramic element to the water.
Nautical Mile 6,076 feet or 1.15 statute
miles.
Ohm a unit of resistance to an electrical
current. Some materials conduct electricity readily while others are poor conductors. The poorness of the conductivity is
the resistance of the molecular structure
to carrying the electrical current.
20
Original Equipment Manufacturer
(OEM) These are the businesses that buy
our product for use with their manufactured products.
Performance Requirement the work
that a customer needs the transducer to
do, e.g. see a narrow but deep area or
measure speed and temperatures in salt
water below 32° F.
Personal Water Craft (PWC) a jet-ski
type recreational water vehicle.
Phased Array a series of piezoceramic
elements in a transducer. The piezoceramic elements are wired in a manner
which allows them to fire in time
delayed sequence, so the echosounder
can electronically steer the array.
Piezoceramic Element a material
made of crystals with positive and negative charges. Frequently referred to as a
piezoceramic or ceramic.
Polarize the ability to align electrically
charged crystals placing like poles in the
same direction.
Pole one end of polarized material, i.e.
the positive pole of a piezoceramic element.
Potting Material see Encapsulant
Projector when the transducer acts as
a transmitter only. This is the case with
the dB PLUS™ II Acoustic Deterrent
System.
“Q” an abbreviation for quality. A measure of how tolerant a transducer is to
changes in frequency.
Radiation Pattern outline of sound
waves as they travel outwards from a
transducer, usually represented as a
cone shape.
Receiving Voltage Response (RVR)
the measure of the voltage produced
within the transducer when returning
echoes are received.
Resistor an electrical component used
to limit the amount of an electrical current passing through it. The level of this
limitation is measured in ohms.
Glossary of Terms
Resolution the ability to show fine
detail. Better resolution provides better
discrimination among individual objects.
Resonant the natural tendency of a
material to vibrate at its own favored
rate (frequency).
Ring Down the tapering off of the vibrations from a transmit pulse. The vibrations may interfere with the reception of
accurate information by the transducer
and thereby distort the information displayed by the echosounder screen.
Ringing the continued vibration of a
piezoceramic element beyond the electrical transmit pulse. This causes distorted information to be displayed on the
echosounder screen.
SEALCAST™ an Airmar trademarked
name for a transducer housed in one
seamless unit.
Sensor any device that detects and
responds to a stimulus such as temperature, speed, motion, light, various chemicals, etc.
Shielding material used to prevent
interference from other electrical equipment on the boat or in the area that
could interfere with the workings of the
transducer.
Sidelobes those portions of the acoustic
signal that are located outside the main
sound beam.
Smear/Smearing distorted information, specifically a running together of
fish images displayed by the
echosounder system because of unwanted sound waves.
Sonar derived from the words sound
navigation ranging. An apparatus that
uses reflected sound waves to detect
and locate underwater objects.
Sound Field the total area where sound
waves travel from a transmit pulse. The
sound field includes the main beam and
sidelobes as well as spurious radiation.
Sound Isolating Material usually a
layer of cork or foam that surrounds the
piezoceramic element except where it
comes in contact with the acoustic window. This is done to focus the sound
waves in one direction and prevent spurious radiation.
Speed Sensor a device that detects the
rate of speed of a water craft.
Spurious Radiation sound waves that
escape in non-desired directions. This
produces false readings by the
echosounder system.
Target Masking the areas within a
transducer’s range which seem to be
invisible to the transducer.
Temperature Sensor a device that
detects the temperature of water.
Thermal Conductor a material with the
ability to let heat travel through it. A
good thermal conductor adjusts quickly
to the temperature of its environment.
Thermistor a unit for sensing and measuring temperature.
Thru-hull Installation a method for
installing a transducer through a hole in
the hull of a boat.
Transducer a device that changes electrical energy to acoustic energy and
back again. This function is performed
by a piezoceramic element(s).
Transmit Pulse a usually brief sequence
of sound waves sent out by the transducer. Following the transmit pulse
there is a longer period of time when
the transducer stops transmitting and
receives the echoes.
Transmitting Voltage Response (TVR)
the pressure or “loudness” of a sound
wave produced by one volt of electricity.
Transom Mount Installation a method
for installing a transducer on the back
(transom) of a boat hull.
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TRIDUCER® Multisensor an Airmar
trademarked name for a sensor that can
measure three functions: depth, speed,
and temperature in one unit. Airmar has
been granted a patent for TRIDUCER®
multisensors and has sole rights to this
design.
Ultrasonic sound waves of high frequency than cannot be heard by
humans. Sound waves higher than
20,000 Hertz.
Volt a unit of electrical force.
Voltage a measure of electrical force or
the potential for current to flow.
Work the effect of force acting on a
body. It is the relationship between the
application of a force to an object and
the distance that object moves when
the force is applied. It is calculated by
multiplying the force times the distance
the object is moved.
Theory of Operations
AIRMAR
TECHNOLOGY CORPORATION
35 Meadowbrook Drive, Milford, New Hampshire 03055
Tel 603 -673-9570 • Fax 603-673-4624• www.airmar.com
17-256-01 Rev. 01
AIRMAR
TECHNOLOGY CORPORATION